This application claims priority under 35 USC 119 from Japanese Patent Application No. 2003-80948, the disclosures of which are incorporated by reference herein.
1. Field of the Invention
The present invention relates to an inkjet recording head and an inkjet recording device.
2. Description of the Related Art
An inkjet recording device records text, images and the like on recording paper by reciprocating an inkjet recording head in a main scanning direction, conveying the recording paper in a sub-scanning direction, and selectively discharging ink droplets from a plurality of nozzles. A technology is well known in which an inkjet recording head discharges an ink droplet from a nozzle that communicates with a pressure chamber by applying pressure, via an oscillating diaphragm, to ink in the pressure chamber by using an actuator such as, for example, a piezoelectric element which converts electrical energy to mechanical energy.
In recent years, the trend for inkjet recording devices to get faster has intensified. Accordingly, inkjet recording heads which are capable of image formation over broader regions in shorter times have been produced by lengthening the inkjet recording heads, increasing the number of nozzles at each inkjet recording head, and arraying the nozzles in matrix patterns (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-334661).
When an inkjet recording head is lengthened and the nozzles are increased in number and arrayed in a matrix pattern as described above, a large number of piezoelectric elements arrayed in the matrix pattern are also required in accordance therewith. This large number of piezoelectric elements arrayed in the matrix pattern are formed by machining, for example, by sandblasting, a single piezoelectric plate (i.e., by machining a piezoelectric material such as a piezoelectric ceramic plate or the like, prior to preparation of the piezoelectric elements). Therefore, the longer the inkjet recording head, the longer the piezoelectric plate for forming the piezoelectric elements. However, making the piezoelectric plate longer and forming the large number of piezoelectric elements arrayed in the matrix pattern is problematic for manufacturing, and leads to a decrease in yields.
Accordingly, a technique has been considered in which a plurality of actuator units, at which the piezoelectric elements are formed, are connected in a row direction of the nozzles for lengthening. With such a structure, the large number of piezoelectric elements are formed so as to be divided up between a plurality of piezoelectric plates. In consequence, the decrease in yields does not result.
However, in a case in which a plurality of actuator units are thus joined for lengthening, problems may arise in assembly if there is no spacing at joining portions thereof. Accordingly, there is a technique in which a plurality of parallelogram-form actuator units are offset in the main scanning direction and a spacing L between the actuator units is assured (see, for example, JP-A No. 10-217452).
However, it is necessary to dispose the parallelogram-form actuator units to be offset in the main scanning direction in order to assure the spacing L between the actuator units. Consequently, the width in the main scanning direction of the inlkjet recording head in which the actuator units are joined becomes larger in accordance with lengthening of the inkjet recording head (see FIG. 1 of JP-A No. 10-217452). As a result, the inkjet recording head becomes larger together with the length of the inkjet recording head.
The present invention has been devised in order to solve the problems described above, and an object of the present invention is to lengthen an inkjet recording head while assuring assembly characteristics and not increasing width of the inkjet recording head, and without causing a deterioration in yield.
In a first aspect of the present invention, an inkjet recording head which scans in a direction intersecting a conveyance direction of a recording medium and records an image at the recording medium with ink drops ejected from nozzles includes: a nozzle plate in which the nozzles which eject the ink drops are formed; pressure chambers communicating with the nozzles; actuators abutting at the pressure chambers, which at least one of increase and reduce pressures of ink in the pressure chambers; and a plurality of nozzle rows parallel to the conveyance direction of the recording medium. This inkjet recording head includes at least two nozzle groups which are grouped over a plurality of the nozzle rows, and each nozzle group is offset, relative to a neighboring nozzle group, in a direction intersecting a row direction of the nozzle rows such that the nozzle groups are arranged in a staggered form, and the numbers of nozzles in the nozzle rows of each nozzle group decrease in the direction intersecting the row direction, from the nozzle row at a side furthest from the neighboring nozzle group to the nozzle row at a side closest to the neighboring nozzle group.
According to an inkjet recording head of the present aspect, the at least two nozzle groups, which are grouped traversing the plurality of nozzle rows, are included. The nozzle groups are disposed in a staggered pattern and separated from one another in the direction intersecting the row direction of the nozzle rows. The number of nozzles in each nozzle row becomes smaller in accordance with progress from a first of the nozzle rows to a last of the nozzle rows along the direction in which the nozzle groups are separated from one another. Thus, gaps can be formed between the nozzle groups.
Because the gaps can be formed between the nozzle groups, if actuator units are formed by machining for each nozzle group and these actuator units are joined to produce the inkjet recording head, there is not a problem with assembly.
Further, these actuator units are formed by machining a plurality of short actuator plates (an actuator material prior to machining of the actuators), which oppose the nozzle groups. Thus, in contrast to long piezoelectric plates, a deterioration in production yields does not result.
Furthermore, the nozzle groups are arranged in the staggered pattern and the nozzle groups are only offset forwards and backwards in the scanning direction of the inkjet recording head. Thus, if the actuators are increased in number in accordance with lengthening of the inkjet recording head, the width of the inkjet recording head will not increase therewith.
In a second aspect of the present invention, an inkjet recording head which records an image over a width of a recording medium, which is being conveyed, with ink drops ejected from nozzles includes: a nozzle plate in which the nozzles which eject the ink drops are formed; pressure chambers communicating with the nozzles; actuators abutting at the pressure chambers, which at least one of increase and reduce pressures of ink in the pressure chambers; and a plurality of nozzle rows in a direction intersecting the conveyance direction of the recording medium. This inkjet recording head includes at least two nozzle groups which are grouped over a plurality of the nozzle rows, and each nozzle group is offset, relative to a neighboring nozzle group, in a direction intersecting a row direction of the nozzle rows such that the nozzle groups are arranged in a staggered form, and the numbers of nozzles in the nozzle rows of each nozzle group decrease in the direction intersecting the row direction, from the nozzle row at a side furthest from the neighboring nozzle group to the nozzle row at a side closest to the neighboring nozzle group.
According to the present aspect, the same effects as in the first aspect described above are obtained. Further, the inkjet recording head is fixed but can record images over the width of the recording medium that is being conveyed. Thus, an inkjet recording head capable of high-speed printing can be provided.
In a third aspect of the present invention, when viewed in the row direction of the nozzle rows, the nozzles of the nozzle groups are disposed to line up in the row direction.
According to the present aspect, the nozzle groups overlap if viewed in the row direction of the nozzle rows. Thus, the width of the inkjet recording head does not increase as in a conventional example (the structure in FIG. 1 of JP-A No. 10-217452).
In a fourth aspect of the present invention, arrangement forms of the nozzles of the nozzle groups include, when straight lines are taken between the nozzles disposed at outer edges of the nozzle groups, at least one of a triangular form and a trapezoid form.
In a fifth aspect of the present invention, arrangement forms of the nozzles of the nozzle groups are such that the nozzle groups include a combination of forms including a plurality of nozzle groups with the at least one of a triangular form and a trapezoid form.
In a sixth aspect of the present invention, actuator units, which are structured to include at least the pressure chambers and actuators respectively corresponding to the nozzles constituting the nozzle groups, are included one at each nozzle group.
According to the present aspect, the actuator units described above are provided one for each nozzle group, and actuator characteristics tests for predicting ink drop discharge characteristics can be carried out on each actuator unit. Thus, the occurrence or absence of failures at each actuator unit, characteristics thereof and the like can be found out by carrying out the actuator characteristics tests on each actuator unit prior to assembly. Therefore, by appropriately selecting the actuator units, co-ordinating the characteristics of the actuator units and assembling the same, ink droplet discharge characteristics of the inkjet recording head can be made uniform.
In a seventh aspect of the present invention, each nozzle group is provided with an ink discharge unit including at least the nozzle plate and the actuator unit.
According to the present aspect, each nozzle group is provided with the ink discharge unit with the structure described above. Hence, ink droplets can be discharged at the ink discharge units. Further, because, as mentioned above, the gaps are formed between the nozzle groups, the ink discharge units can be associated in the staggered form to structure the inkjet recording head. Thus, the inkjet recording head can be lengthened without increasing the width of the inkjet recording head. Moreover, in cases in which problems arise, the ink discharge units can be individually replaced.
In an eighth aspect of the present invention, the actuators include piezoelectric elements for converting electrical energy to mechanical energy.
In a ninth aspect of the present invention, the actuators include heatgenerating resistors which pressurize the ink in the pressure chambers by heating and causing bubbling.
In a tenth aspect of the present invention, an inkjet recording device employs an inkjet recording head included in the aspects described hereabove.
Because an inkjet recording device based on the present aspect employs an inkjet recording head included in the aspects described above, the width of the inkjet recording head is not increased, and the inkjet recording device is not made larger.